﻿424 
  B. 
  A. 
  Daly 
  — 
  Geology 
  of 
  Pigeon 
  Point, 
  Minnesota. 
  

  

  because 
  transportation 
  by 
  the 
  motor-boats 
  of 
  resident 
  fishermen 
  

   could 
  be 
  secured. 
  

  

  The 
  objects 
  of 
  the 
  visit 
  were 
  to 
  secure 
  personal 
  acquaintance 
  

   with 
  the 
  rocks 
  so 
  admirably 
  described 
  by 
  Bayley, 
  and 
  to 
  collect 
  

   structural 
  and 
  petrographical 
  material 
  bearing 
  on 
  the 
  origin 
  of 
  

   the 
  local 
  " 
  red 
  rock," 
  which 
  represents 
  one 
  of 
  the 
  main 
  prob- 
  

   lems 
  of 
  Minnesota 
  geology 
  and, 
  yet 
  more 
  significantly, 
  falls 
  

   under 
  the 
  general 
  question 
  regarding 
  the 
  origin 
  of 
  the 
  world's 
  

   granites. 
  

  

  The 
  red 
  rock 
  has 
  been 
  called 
  " 
  quartz 
  keratophyre 
  " 
  and 
  also 
  

   " 
  soda 
  granite." 
  It 
  is 
  a 
  highly 
  micropegmatitic 
  or 
  granophyric 
  

   rock, 
  chemically 
  very 
  similar 
  to 
  many 
  common 
  granites, 
  but 
  

   locally 
  it 
  has 
  a 
  chemical 
  composition 
  much 
  like 
  a 
  quartz 
  sye- 
  

   nite. 
  The 
  red 
  rock 
  passes 
  gradually 
  into 
  " 
  intermediate 
  rock," 
  

   that 
  varies, 
  chemically, 
  from 
  a 
  monzonito-like 
  type 
  to 
  a 
  diorite- 
  

   like 
  type. 
  The 
  intermediate 
  rock, 
  always 
  in 
  small 
  volume, 
  in 
  

   turn 
  grades 
  into 
  gabbro. 
  The 
  latter 
  is 
  much 
  the 
  largest 
  com- 
  

   ponent 
  of 
  the 
  main 
  Pigeon 
  Point 
  intrusive. 
  It 
  has 
  olivine-rich 
  

   and 
  olivine-free 
  phases. 
  Though 
  possessing 
  a 
  somewhat 
  low 
  

   content 
  of 
  alkalies, 
  the 
  gabbro 
  has 
  nearly 
  normal 
  characters. 
  

   For 
  the 
  full 
  petrography 
  of 
  the 
  eruptive 
  and 
  sedimentary 
  rocks 
  

   of 
  the 
  point, 
  the 
  reader 
  is 
  referred 
  to 
  Bayley's 
  memoir. 
  

  

  Short 
  as 
  the 
  field 
  study 
  was, 
  it 
  permitted 
  a 
  revision 
  of 
  the 
  

   geological 
  map 
  and 
  structure 
  sections 
  published 
  in 
  Plate 
  XVI 
  

   of 
  Bayley's 
  paper. 
  A 
  map 
  showing 
  necessary 
  changes 
  in 
  the 
  

   lines 
  of 
  contact 
  is 
  given 
  in 
  the 
  accompanying 
  fig. 
  1. 
  So 
  far 
  as 
  

   the 
  outcrops 
  allow 
  a 
  decision, 
  the 
  main 
  intrusive 
  appears 
  to 
  be 
  

   a 
  sill 
  cutting 
  the 
  local 
  Animikie 
  sedimentaries, 
  rather 
  than 
  a 
  

   dike, 
  as 
  stated 
  by 
  Bayley. 
  The 
  red 
  rock 
  is 
  concluded 
  to 
  be 
  a 
  

   gravitative 
  differentiate 
  from 
  the 
  magma 
  which 
  filled 
  the 
  sill 
  

   chamber. 
  As 
  Bayley 
  and 
  others 
  proved 
  long 
  ago, 
  the 
  origin 
  

   of 
  that 
  magma 
  is 
  a 
  question 
  involving 
  the 
  possibility 
  of 
  the 
  

   fusion 
  of 
  the 
  Animikie 
  quartzites 
  and 
  metargillites 
  by 
  primary 
  

   gabbroid 
  magma. 
  While 
  Bayley 
  showed 
  the 
  probable 
  reality 
  

   of 
  this 
  melting-up, 
  its 
  absolute 
  proof, 
  here 
  as 
  so 
  commonly 
  at 
  

   eruptive 
  contacts, 
  is 
  obscured 
  by 
  the 
  processes 
  of 
  differentia- 
  

   tion. 
  

  

  A 
  special 
  novelty 
  discovered 
  is 
  the 
  existence 
  of 
  minute 
  igne- 
  

   ous 
  bodies 
  which 
  are 
  hereafter 
  described 
  under 
  the 
  name 
  

   "linear 
  or 
  ribbon 
  injections." 
  

  

  Professors 
  Palache 
  and 
  Grout 
  have 
  greatly 
  aided 
  in 
  the 
  col- 
  

   lection 
  of 
  facts 
  and 
  in 
  clarifying 
  the 
  discussion, 
  but 
  neither 
  

   should 
  be 
  held 
  responsible 
  for 
  the 
  theoretical 
  views 
  hereafter 
  

   expressed. 
  

  

  Revised 
  Map. 
  — 
  Pigeon 
  Point 
  is 
  a 
  peninsula 
  stretching 
  east- 
  

   ward 
  from 
  the 
  main 
  shore 
  of 
  Lake 
  Superior, 
  150 
  statute 
  miles 
  

   (240 
  kilometers) 
  northeast 
  of 
  Duluth. 
  The 
  peninsula 
  is 
  six 
  

  

  